Project summary Articular cartilage lesions are prevalent disorders affecting millions of Americans. Deprived of spontaneous healing capacity, cartilage lesions may further deteriorate and lead to the onset of osteoarthritis (OA). OA represents a leading cause of chronic disabilities in the U.S. and ultimately warrants total joint arthroplasty. A common aspiration in orthopedic medicine is to regenerate the damaged articular cartilage. Currently, arthroscopic microfracture is a popular clinical procedure that debrides damaged cartilage tissue and induces bleeding from bone marrow to fill cartilage defects. However, microfracture yields fibrous tissue or fibrocartilage at best, which has inferior mechanical properties than articular hyaline cartilage. Previous work, including our preliminary data, demonstrates that certain cytokines such as transforming growth factor beta 1 and 3 (TGF?1 and TGF?3) induces hyaline cartilage formation by endogenous cells. Specifically, we showed that delivery of exogenous TGF?3 in an anatomically correct, porous scaffold, without cell transplantation, was sufficient for the regeneration of an entire articular cartilage layer in vivo, with functional recovery. A substantial barrier towards translation of existing work into a clinical therapy is the cost of exogenous growth factors (proteins and peptides) and development of growth factors as a product. The literature shows that the synovial joint harbors substantial amounts of TGF?s, but in latent forms. The innate TGF?s in latent forms are dormant in homeostasis but are activated upon injury or tissue repair. Our preliminary work further demonstrated that ascorbate can readily activate latent TGF?s in a way that can be harnessed towards repair of focal cartilage defects in a rabbit model and also avoid the OA development in a rat model. Our central hypothesis that endogenous, latent TGF?s in synovial fluid and other joint tissues, when focally activated at defect site, may induce repair of cartilage defects. Together, our preliminary studies strongly suggest that ascorbate can be locally delivered to activate latent TGF?s in a way that benefit cartilage regeneration in focal defects. The overall objective of the present SBIR Phase I proposal is to improve the ascorbate laden prototypes for optimal pro-chondrogenesis. The benefit of this approach as an adjunctive procedure of the current clinical gold standard of arthroscopy procedures is a substantial factor in favor of translation ultimately towards clinical application.